Subjects The investigators plan to enroll 50 children who are participants in outpatient weight-loss programs in the German part of Switzerland. Enrollment will be done with the agreement and assistance of the physician supervising the weight-loss program, and the timing of the study measurements will be incorporated within the existing program schedule. It is anticipated that the baseline blood sample for this study will be obtained from the regular baseline venipuncture for the weight-loss study. Criteria for participation include age between 10 to 18 years and a BMI over the 85th percentile for age and sex. Exclusion criteria include major medical illnesses, including gastrointestinal, inflammatory, bleeding and/or endocrine disorders, a history of nephrolithiasis, unusual dietary habits (e.g. vegetarianism), major food allergies or intolerances (lactose, gluten), smoking, and use of chronic medications or vitamin/mineral antioxidant supplements.